Laser Straight Liner is usually adapted for use in the field of construction and decoration layout, mainly including a foundation and a base, wherein said base is provided with laser projection modules. In practical use, these existing Laser Straight Liners normally suffer from some certain disadvantages that the laser beam emitted by the instrument is permanently fixed relative to the instrument itself, and in order to rotate the angle during marking, user must turn the whole instrument. In this way the position of the straight liner may easily suffer from deviation, and thus the marking error occurs. Moreover, those straight liners are not convenient for user to get the desired rotated angle.